The present invention relates generally to window films and, more particularly, to sealing the seam between the adjacent edges of window films including a metal layer.
Window films are commonly used in commercial buildings, residential homes, and in automotive applications to save energy, improve comfort, provide UV protection, prevent the leakage of high frequency communications signals from the structure, and to help reduce the dangers associated with window breakage. Window films are commercially available from 3M Company, St. Paul, Minn., under, for example, the Scotchtint window film product designation.
Many window film constructions include a metal layer, such as a vapor deposited layer of silver. High conductivity of the metal layer is desirable where the window film is to be used to prevent leakage of high frequency (e.g. 100 MHz-6 GHz) communication signals from the structure. In order to achieve a window film having the best combination of high conductivity, high transmission and high reflection, it is desirable to use pure silver for the metal layer.
Silver layers are highly prone to corrosion in the presence of atmospheric elements such as water and chlorine, particularly along the edges of the window film. That is, even though the layer of silver of a window film may be protected by a coating or a laminated film, the silver layer will be exposed to the corrosive elements of the surrounding environment along its edges. The corrosion process is accelerated with increased ambient temperature in the presence of salt and moisture. Corrosion is aesthetically undesirable and also interferes with the performance of the window film. To protect it from corrosion, the silver layer may be alloyed or sandwiched between layers of other metals, such as copper or gold. These corrosion protection methods, however, add cost to the window film, alter the appearance and optical transmission of the window film, and decrease the conductivity of the metal layer.
In many instances, a window film having low reflection in the visible part of the solar spectrum (400-800 nm) is desirable while maintaining a high degree of reflection in the near infrared (IR) range (800 nm-2500 nm). Multi-layer window film constructions having a dielectric/metal/dielectric in an A/B/A/B . . . type sequence may be made by tailoring the thickness of the individual layers such that the reflection in the visible range is suppressed. Such films are described in, for example, U.S. Pat. Nos. 6,007,901 (Maschwitz, et al.) and 6,391,400 (Russell, et al.).
In many applications, the size of the window exceeds the size of the available window film. For example, a window may be 84 inch×96 inch in size while the widest available window films typically have a width of only 60 inches. In such cases, more than one piece of window film is required to cover the entire glass pane, thereby resulting in a seam. Untreated seams are susceptible to corrosion when the window films contain metal layers, such as silver, and must, therefore, be protected. Typically, a thin bead of sealant is used to seal the seam in such cases. Such sealants, however, may allow infrared or other electromagnetic radiation to leak through the seam. A dark sealant material—which absorbs IR radiation—may be used to seal the seam, but the dark appearance of the sealant is often considered aesthetically objectionable.
U.S. Pat. No. 4,645,714 (Roche) discloses durable, specularly reflective mirrors for solar reflectors or fluorescent lamp fixtures that are formed by vapor-depositing silver on a polyester film and protectively covering it with a coating of transparent acrylate polymer containing a silver corrosion inhibitor such as glycol dimercaptoacetate.
U.S. Pat. No. 6,090,451 (Barth et al.) discloses edge sealing a window film by moving a porous applicator tip saturated with liquid sealant in wiping contact along an edge of the window film to be sealed so as to transfer a portion of the liquid sealant from the saturated applicator tip to the window film edge.
U.S. Pat. No. 6,294,233 (Barth et. al.) discloses transparent edge sealed window films. The edges of the window films are preferably sealed by a liquid solvated polymer material which, upon curing, provides a solid transparent seal which significantly minimizes the degradative effects of the ambient environment.
The need generally exists for a way to eliminate the problems of corrosion and/or unwanted leakage of electromagnetic radiation associated with seams formed by the adjacent edges of window films that include a metal layer. More specifically, the need exists for a sealing tape that prevents corrosion and unwanted leakage of electromagnetic radiation associated with such seams. The need also exists for a method that allows two individual sheets of window film to be applied to a window without creating a seam between the adjacent edges of the window films that is prone to corrosion. That is, the need exists for a method of applying at least two individual sheets of window film to a window, wherein at least one of the window films includes an internal metal layer, in a manner that the seam formed between the adjacent edges of the window films is protected or otherwise rendered corrosion resistant. The need also exists for a method of preventing IR radiation from leaking through such a seam. The need also exists for a fast, easy, inexpensive, and effective method of rendering a seam between adjacent edges of a window film corrosion resistant and resistant to IR leakage, and which does not otherwise interfere with the performance and/or appearance of the window film.